The present invention relates to a method of vaccinating domesticated birds against coccidiosis. In particular, the invention relates to the in ovo administration of live Eimeria spp sporozoites or merozoites, or mixtures thereof, into the developing eggs of domesticated birds in order to immunize the hatched chicks against coccidiosis.
Coccidiosis is an enteric disease of domesticated birds caused by infection with intracellular protozoan parasites of the genus Eimeria. Coccidiosis is the most economically devastating parasitic disease of domesticated birds. It is estimated that anticoccidial medications and losses due to coccidiosis cost the poultry industry hundreds of millions of dollars every year.
Various attempts to vaccinate domesticated birds against coccidiosis have been reported since the early 1950's. Current vaccination methods include administering live Eimeria oocysts to birds through feed or water. These methods, however, are inconvenient and inefficient because not all birds get the intended oocyst dose and many are either unprotected by the vaccine or receive a pathogenic infection.
In J. M. Sharma and B. R. Burmester, Avian Dis. 26: 134–149, 1981, the authors reported that chickens vaccinated in ovo with herpesvirus of turkey developed immunity against subsequent challenge with Marek's disease virus. In European patent publication no. 291173, an immunization process is referred to wherein a nonreplicating immunogen is administered in ovo. The immunogens specifically referred to in the European patent are a genetically engineered Eimeria antigen and an Eimeria oocyst extract. The European patent specifically excludes live parasite stages such as those used in the vaccination method claimed herein.
The present vaccination method involves in ovo administration of live Eimeria sporozoites or merozoites, or a mixture thereof, into the developing eggs of domesticated birds. The available literature suggests that such a vaccination method would be ineffective in ovo and should be applied post-hatch. In T. K. Jeffers and G. E. Wagenbach, J. Parasit. 56(4): 656–662, 1970, the authors reported that in ovo injection of E. tenella sporozoites on day 10 of incubation provided no significant immunological protection against subsequent challenge with E. tenella oocysts. In fact, they reported that chicks that received no treatment had a greater survival rate against subsequent challenge with E. tenella oocysts than chicks that had been treated in ovo with sporozoites. In K. L. Watkins et al., Proc. VI th. International Coccidiosis Conf., Abstract E1–2, Ontario, Canada, 1993, the authors described in ovo inoculation with live E. maxima sporocysts and sporulated oocysts and concluded that their study provided no evidence that in ovo exposure protects against subsequent coccidial challenge with E. maxima oocysts 10 days post-hatch. Watkins et al. further concluded that significant immunological protection is provided if inoculation is done soon after hatch rather than in ovo. Contrary to this teaching, the in ovo vaccination method of the present invention provides unexpected immunity that protects the hatched birds against subsequent coccidial challenge.